1. Field of the Invention
The present invention relates to a power distribution scheme in a portable computer and, more specifically, to power management in a laptop computer.
2. Prior Art
Power consumption in an electronic device is always a significant concern and a power supply must be designed to adequately power the device. Aside from the capability of the power supply to provide ample power to power the corresponding device, heat dissipation, physical size, weight, efficiency, and other related characteristics are paramount in designing or selecting the power source. These characteristics become exceptionally critical when the device the power supply is to support is a self-sufficient portable unit.
In many portable units, a self-supporting power source, such as a battery, is used to provide the power when the unit is decoupled from its main or external power source, such as 110 Volt AC (ordinary house current). Typically a battery is used to provide the independent and portable power source. In some instances the battery functions as an auxiliary power source to maintain certain critical circuits active, such as keeping the memory alive to retain any information stored in the memory. In other instances, the battery functions as the main power source to fully power the device.
In the area of information processing, miniaturization of processing devices has permitted the portability of computing devices. One of the first such portable processing devices was a hand held calculator, wherein the calculator operated from a battery power source and could easily be carried about by the user. The battery would power all of the functions of the calculator and the user could readily transport the calculator without any attachment to an external power source. The batteries were either replaced or recharged. The earliest calculators simply had an on/off state in which full power was available during the on state and the power was completely shut off during the off state. Bacause of the volatile nature of many early semiconductor memories, information stored in such volatile memories were lost when the calculator was turned off. Subsequent calculators attempted to incorporate nonvolatile memory, or in the alternative, standby power was provided to such a memory when the device was turned off, so that the memory retained whatever information was present. More advanced schemes were devised to monitor various functions, so that power was removed from various elements when those elements were not needed. Further, a time-out scheme was devised to put the calculator in a stand-by mode, such as when a key was not depressed after a certain time period, in order to preserve power. All of these features were devised primarily to extend the time period that the device could operate from its internal power source.
When the processing technology was expanded beyond a simple calculator to encompass personal desk top computers, additional constraints were placed to power consumption and management control schemes. Aside from the additional circuitry, additional memory devices consumed considerable amounts of power. These memory devices include semiconductor devices, such as read-only memories (ROMs) and random-access memories (RAMs) which include volatile and non-volatile memories, floppy disk drives and hard disk drives and other magnetic media. Also, additional power is required to power the display unit which typically includes a viewing screen. Various schemes were devised to monitor and control the power distribution during on/off states.
However, as the personal desk top computer systems are made portable, it is desirable to provide a computer which contains a fully contained power source so that the computer is completely portable. These self-sufficient computer systems are typically referred to as laptops (because of the small physical size and light weight) and are designed to operate for a certain number of hours from its internal power source, which is typically a battery. Although a variety of the portable calculator technology can be implemented within such a laptop, additional constraints are placed in that the additional circuitry, memory, viewing screen and any peripheral devices attached to the system will necessarily consume additional power. In order to extend the self-sustaining time period of these laptops while keeping the battery size and weight to a minimum, a sophisticated power management scheme is required to provide power only to those circuits and devices which require such power and to remove power, or at least to make a given circuit enter a low power consumption mode, when that circuit is not needed. The management scheme must also continually monitor the various circuits and devices in order that power can be applied immediately to activate such circuits and devices when needed.
The present invention provides for such a power management apparatus for a laptop computer in order to extend the self-sustaining time period so that the laptop computer can operate for an extended period of time once external power is disconnected.